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1. Field of the Invention
The present invention generally relates to a self-adjust pawl and ratchet mechanism for a parking brake system and, more particularly, to such a mechanism which ensures positive full engagement between the pawl and the ratchet.
2. Background of the Invention
It is well known in the prior art for a vehicle parking brake system to include self-adjust means for automatically disengaging a brake cable from an operating handle or lever when the lever is in a brake release position in order to remove slack from the brake cable. For example, see U.S. Pat. Nos. 4,841,798, 4,872,368, 5,001,942, 5,235,867, and 5,467,666, the disclosures of which are expressly incorporated herein in their entirety by reference.
In these known self-adjust means, an adjuster pawl and ratchet are provided in addition to the main pawl and ratchet. Typically, the brake cable is connected to the adjuster ratchet and the adjuster pawl is pivotally mounted to the operating lever whereby load is transferred from the ratchet to the operating lever via the pawl and its pivot pin. The adjuster pawl is automatically released from the adjuster ratchet when the operating lever is returned to the brake-release position. If the adjuster pawl is only partially engaged with the adjuster ratchet, a tooth may chip and/or slip out of engagement when subjected to full system load.
In an attempt to solve this problem and provide positive full engagement between the adjuster pawl and ratchet teeth, cam-out and cam-in pins or abutments were developed. It is customary to provide the cam-out pin or abutment on the housing to positively disengage the adjuster pawl from the adjuster ratchet when the operating lever is moved to the brake-release position. When the operating lever is pivoted toward the brake-engaging position, the spring-biased adjuster pawl automatically pivots toward engagement with the adjuster ratchet. The cam-in pin or abutment is typically provided to positively engage the adjuster pawl with the adjuster ratchet when the operating lever is moved to the brake-applied position. The cam-out and cam-in surfaces are preferably shaped and positioned to achieve full engagement between the adjuster pawl and the adjuster ratchet by eliminating top-on-top and partial-engagement conditions between the teeth. While these attempts may be somewhat successful, partial engagement and accidental disengagement of the adjuster pawl still occurs. Accidental disengagement and/or partial engagement can still be a problem due to tolerances of components and/or deflection of components. Accordingly, there is a need in the art for an improved adjuster mechanism for a parking brake system which reduces and/or eliminates partial engagement and/or accidental disengagement.
The present invention provides a parking brake system which overcomes at least some of the above-noted problems of the related art. According to the present invention, a parking brake system of the self-adjust type for automatically removing slack from a parking brake cable includes, in combination, a fixed support and a lever pivotably connected to the support for movement between brake-releasing and brake-engaging positions. A locking mechanism releasably maintains the lever in the brake-engaging position. The locking mechanism includes a main ratchet fixed relative to the support and having a plurality of ratchet teeth and a main pawl pivotably connected with the lever and having a pawl tooth for releasable engagement with the ratchet teeth of the main ratchet. A self-adjust mechanism releasably connects the parking brake cable with the lever. The self-adjust mechanism includes an adjuster ratchet connected to the parking brake cable and having a plurality of ratchet teeth and an adjuster pawl pivotably connected with the lever and having at least one pawl tooth releasably engaging the ratchet teeth of the adjuster ratchet. The adjuster pawl is pivotable relative to the lever about a pivot axis. A pawl spring member biases the adjuster pawl toward engagement with the adjuster ratchet. The adjuster pawl has an approach angle extending between a tangential force direction and a force direction from a tooth contact point engaging the adjuster ratchet to the pivot axis of the adjuster pawl. The approach angle is greater than 45 degrees and preferably within the range of about 55 degrees to about 75 degrees.
According to another aspect of the present invention, a parking brake system of the self-adjust type for automatically removing slack from a parking brake cable includes, in combination, a fixed support and a lever pivotably connected to the support for movement between brake-releasing and brake-engaging positions. A locking mechanism releasably maintains the lever in the brake-engaging position. The locking mechanism includes a main ratchet fixed relative to the support and having a plurality of ratchet teeth and a main pawl pivotably connected with the lever and having a pawl tooth releasably engaging the plurality ratchet teeth of the main ratchet. A self-adjust mechanism releasably connects the parking brake cable with the lever. The self-adjust mechanism includes an adjuster ratchet connected to the parking brake cable and having a plurality of ratchet teeth and an adjuster pawl pivotably connected with the lever and having a plurality of pawl teeth releasably engaging the plurality of ratchet teeth of the adjuster ratchet. A pawl spring member biases the adjuster pawl toward engagement with the adjuster ratchet. The plurality of pawl teeth of the adjuster pawl are adapted such that only one of the plurality of pawl teeth of the adjuster pawl fully engages the plurality ratchet teeth of the adjuster ratchet at any given time. Preferably, the plurality of pawl teeth of the adjuster pawl are spaced side-by-side to form a substantially linear row and the plurality of ratchet teeth of the adjuster ratchet are spaced side-by-side to form a substantially arcuate row.
According to yet another aspect of the present invention, a parking brake system of the self-adjust type for automatically removing slack from a parking brake cable includes, in combination, a fixed support and a hand-operated lever pivotably connected to the support for movement between brake-releasing and brake-engaging positions. A locking mechanism releasably maintains the lever in the brake-engaging position. The locking mechanism includes a main ratchet fixed relative to the support and having a plurality of ratchet teeth and a main pawl pivotably connected with the lever and having a pawl tooth releasably engaging the plurality of ratchet teeth of the main ratchet. A self-adjust mechanism releasably connects the parking brake cable with the lever. The self-adjust mechanism includes an adjuster ratchet connected to the parking brake cable and having a plurality of ratchet teeth and an adjuster pawl pivotably connected with the lever and having three pawl teeth releasably engaging the plurality ratchet teeth of the adjuster ratchet. The adjuster pawl is pivotable relative to the lever about a pivot axis. A pawl spring member biases the adjuster pawl toward engagement with the adjuster ratchet. The adjuster pawl has an approach angle extending between a tangential force direction and a force direction from a tooth contact point engaging the adjuster ratchet to the pivot axis of the adjuster pawl and wherein the approach angle is within the range of about 55 degrees to about 75 degrees. The three pawl teeth of the adjuster pawl are adapted such that only one of the three pawl teeth fully engages the plurality ratchet teeth of the adjuster ratchet at any given time. Preferably, the three pawl teeth of the adjuster pawl are spaced side-by-side to form a substantially linear row and the plurality of ratchet teeth of the adjuster ratchet are spaced side-by-side to form a substantially arcuate row.
From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology and art of parking brake systems. Particularly significant in this regard is the potential the invention affords for providing a high quality, reliable, low cost assembly which does not accidently release the parking brake. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below.